fix: keep a step's own with: values out of its inputs context (#1192)

A step's `if:`, its `continue-on-error:` and its `run:` script resolved `inputs.*` from the step's own `INPUT_*` env. A `with:` key colliding with a workflow input flipped conditions, and any `INPUT_`-shaped variable from `env:` or a `GITHUB_ENV` write forged an input that never existed.

GitHub evaluates all three in the enclosing scope: the workflow inputs, or for a composite action's steps that action's inputs. Action-input interpolation is the one place that legitimately sees a step's own `with:`, so it keeps its own evaluator.

Fixes https://gitea.com/gitea/runner/issues/1191, ports https://github.com/nektos/act/pull/2473 and extends it to the pre and post stages.

---------

Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1192
Reviewed-by: silverwind <[email protected]>
Co-authored-by: ABiscuitttt <[email protected]>

act/runner/run_context_test.go

@@ -992,6 +992,14 @@ func TestRunContextGetEnv(t *testing.T) {
 	}
 }
 
+// a remote composite action re-evaluates its env per stage, so inputs must follow it
+func TestSetActionEnvRefreshesInputs(t *testing.T) {
+	rc := &RunContext{}
+	rc.setActionEnv(map[string]string{"INPUT_MSG": "pre"})
+	rc.setActionEnv(map[string]string{"INPUT_MSG": "main"})
+	assert.Equal(t, map[string]any{"msg": "main"}, rc.actionInputs)
+}
+
 func TestCreateContainerNameBoundedForLongMatrixInput(t *testing.T) {
 	longMatrixValue := strings.Repeat("os=ubuntu-latest-go=1.24-node=22-", 20)
 	name := createContainerName(